Herding mechanisms to maintain the cohesion of a harem group: two interaction phases during herding
In animal groups, individual interactions achieve coordinated movements to maintain cohesion. In horse harem groups, herding is a behavior in which males chase females from behind; it is considered to assist with group cohesiveness. However, the mechanisms by which the individuals move to maintain group cohesion are unknown. We applied novel non-invasive methods of drone filming and video tracking to observe horse movements in the field with high temporal and spatial resolution. We tracked all group members and drew trajectories. We analyzed the movements of females and found two phases of interactions based on their timing of movement initiation. The females that moved first were those nearest to the herding male, while the movement initiation of the later females was determined by the distance from the nearest moving female, not by the distance from the herding male. These interactions are unique among animal group movements and might represent a herding mechanism responsible for maintaining group cohesion. This might be due to long-term stable relationships within a harem group and strong social bonds between females. This study showed that the combination of drone filming and video tracking is a useful method for analyzing the movements of animals simultaneously in high resolution.
KeywordsDrone Video tracking Herding Interaction of individuals Movement Horses
Special thanks to Viana do Castelo city for supporting our project. We are also grateful to Carlos Pereira and Tetsuro Matsuzawa for managing the field work. We also thank Agostinho Costinha, Lourenço Almada, and the villagers in Montaria for their support during our stay. We would like to thank Editage (www.editage.jp) for English language editing.
The study was financially supported by the Japan Society for the Promotion of Science (JSPS) core-to-core CCSN and JSPS-LGP-U04, and Ministry of Education, Culture, Sports, Science and Technology (MEXT) grant No.16H06283 to Tetsuro Matsuzawa, KAKENHI grant Nos. 15H01619, 15H05309, 17H0582, 19H00629, and Kyoto University SPIRITS grant to Shinya Yamamoto, and KAKENHI grant No. 18K18342 to Monamie Ringhofer.
Compliance with ethical standards
All applicable international, national, and institutional guidelines for the care and use of animals were followed. The field observations complied with the guidelines for animal studies in the wild issued by the Wildlife Research Center of Kyoto University, Japan.
Conflict of interest
The authors declared that they have no competing interests.
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